A. Field of the Invention
This invention generally relates to the field of methods and devices for adding, removing and transferring precise volumes of fluid to and/or from a receptacle such as a test tube. These methods and devices are often employed in biological and fluid sample testing machines and related equipment.
The dilution station of the present invention is suitable for use in machines in which a precise volume of fluid (such as a diluent solution or reagent solution) is automatically added to a receptacle for the fluid. The pipetting station is suitable for use in machines which have the need for automatic and accurate removal of a predetermined volume of fluid from a receptacle. While the invention is particularly suitable to automated biological sample testing machines, it is also applicable to other types of machines, as will be more fully understood from the following discussion.
B. Description of Related Art
Automated biological sample testing equipment typically involve the processing of biological samples by multiple modules or "stations", with each station designed to perform a particular function. For example, in the medical area, biological samples are placed in test tubes and processed according to a predetermined methodology.
One common step in the processing of biological samples is the step of adding a fluid to a sample, such as diluting a sample with a diluent, for example, water or saline solution. Prior art techniques for diluting a sample are described in the patents to Douchy et al., U.S. Pat. No. 4,656,007 and Chen, U.S. Pat. No. 4,244,919, and the early patents to Farr, U.S. Pat. Nos. 3,712,754 and 3,567,398.
Another step sometimes found in the processing of biological samples is the removal of fluids from a sample, and the transferring of the removed fluid to another site or receptacle. Representative techniques for handling or removing fluid samples are described in U.S. Pat. No. 4,265,855 to Mandle et al., and the patents to Freeman, U.S. Pat. No. 5,063,790 and Goodman, U.S. Pat. No. 5,343,909.
When samples are to be removed from one receptacle and transferred to another, special problems are encountered. If a pipetting device is used for the removal of fluid, the pipette must be disposed of and a new pipette supplied to the device to avoid contamination between samples. Several patents addressing the challenges of dispensing or handling pipettes and other similarly shaped objects include the patent to Prussi, U.S. Pat. No. 5,100,021, which discloses a package for manual removal of pipettes, and the patents to VanAlstine et al., U.S. Pat. No. 5,265,398; Portyansky, U.S. Pat. No. 4,567,997; Rizzo, U.S. Pat. No. 4,274,194 and Cristiani et al., U.S. Pat. No. 4,270,670.
The present invention overcomes the limitations of the prior art approaches by providing for an efficient and compact arrangement for diluting and pipetting stations. The diluting station provides for precise control of the amount of diluent added to the receptacle, and does not require priming of the diluent addition vessel. The diluting station accomplishes automatic addition of the diluent to the receptacle with a negligible risk of contamination of the diluent or of the diluting apparatus. The pipetting station is particularly advantageous in that it permits disposable straws to be used in the removal of fluids from a sample. The pipetting station achieves the withdrawal of the straws from a hopper and removal of fluid from the receptacle automatically and without human intervention. The pipetting station also accomplishes automatic disposal of the straws after the removed fluid has been transferred to another body, such as to a second receptacle.